1. Field of the Invention
The present invention relates to a fuel injection arrangement for an air-compressing, spontaneous-ignition, internal combustion engine. The arrangement is provided with at least one electromagnetic control valve via which a high-pressure channel of a fuel injection pump, that is provided with an intake line, can be connected with a low-pressure channel, preferably a discharge channel. The control valve comprises a valve body which is in the form of a piston valve, is spring loaded, and is axially movable in a chamber that is provided with at least one high-pressure connection and one low-pressure connection. The piston valve is operatively connected with an electromagnetic adjusting device which can preferably be controlled by an electrically-operating data processor.
A further, preferably mechanically operated, adjustment member may also be provided.
2. Description of the Prior Art
A fuel injection arrangement of the aforementioned general type is known from German Offenlegungsschrift 20 26 665. With this heretofore known arrangement, an electromagnetic control valve, which is controlled by the electrically-operating data processor as a function of characteristic operating parameters of the internal combustion engine, controls a discharge channel provided on the nozzle side in order in particular to regulate the beginning and end of injection of the fuel injection arrangement with regard to the load state of the internal combustion engine. The piston valve of the electromagnetic control valve has the same cross sectional area over its entire length j end faces of the piston valve are acted upon by pump pressure via pressure equalization lines in order in particular to keep low the required magnetic valve actuation adjustment force at the control valve. A drawback to this heretofore known fuel injection arrangement is that the piston valve of the control valve executes uncontrollable movements in the closure position, and hence exhibits an unstable behavior, which can be attributed in particular to a nonuniform pressure application upon the end faces of the piston valve, for example due to varying pressure waves, or to a more or less considerable formation of cavities in the pressure equalization lines. A further drawback is that a more or less considerable formation of cavities in the high-pressure system during control of the nozzle side and further conveyance on the pump side also result in instability with regard to regulation of the injection times.
Also known (German Offenlegungsschrift 29 03 482) is a fuel injection arrangement for an air-compressing, spontaneous-ignition, internal combustion engine according to which an electromagnetically actuated control valve is provided within the injection pump housing for controlling the injection times. On the one hand, this control valve controls the intake line of the injection pump, and on the other hand it connects a discharge channel with a high-pressure channel of the injection pump. The control valve is provided with a valve body which is in the form of a piston valve and is provided with a valve seat. A high-pressure chamber and a low-pressure chamber are provided in the piston valve on both sides of the valve seat. The opposing pressure attack surfaces of the high and low pressure chambers have the same surface area, so that from an ideal static standpoint, the piston valve is pressure balanced in the closure position. However, in addition to the considerable structural expense and the fact that further negative effects, for example caused by a fuel pump, can act via the intake line on the piston valve of the electromagnetic control valve, this heretofore known fuel injection arrangement has the drawback that the pressure forces which act upon the piston valve are only equalized in the closure position, since, during the opening phase of the piston valve, a resulting closure force is generated by a one-sided pressure drop due to the fuel discharging via the valve seat cross sectional area, so that heretoo a precise regulation of the injection process is not possible due to the unstable behavior of the piston valve.
In order to eliminate in particular the aforementioned drawbacks of the unstable behavior of the piston valve of German Offenlegungsschrift 29 03 482 in the opening phase, it was proposed (German Offenlegungsschrift 30 02 361) to give the pressure attack surfaces of the high-pressure chamber of the piston valve different dimensions, and to provide a stationary flow control device in the discharge channel. This solution is also not satisfactory, since, on the one hand, the throttled discharge stands in the way of a rapid pressure reduction at the end of injection in the sense of a favorable consumption and emission characteristic of the internal combustion engine, and, on the other hand, a constant throttling cannot take into account different operating levels of the internal combustion engine due to the respectively different control quantities.
It is therefore an object of the present invention to substantially improve a fuel injection arrangement of the aforementioned general type in such a way that precise control of the injection times is possible.